DIAGNOSING a shorted electrical circuit Electrical issues can 50 PTEN MAY 2016 www.VehicleServicePros.com be some of the most challenging problems to diagnose on today’s vehicles. Not only are there many different causes of electrical faults, but their symptoms can vary as well. Throw in an intermittent issue and it complicates things even more. Common causes of electrical issues are: • High resistance in either power or ground circuits • Open circuits • Shorts to power or ground Tool Briefing TOOLS USED: • Snap-on MicroVat battery tester • Vehicle Repair Information • DMM • ESI Fuse Buddy • Cal-Van Tools Amp Hound 2 • Power Probe IV • Hopkins Tow Doctor • Power Probe ECT2000 Smart Circuit Tracer High resistance in a circuit can cause components to not work correctly such as a starter to crank the engine slower, or a sensor to report the engine temperature incorrectly. High resistance also can cause components to fail prematurely, like a fuel pump due to the pump needing to work harder to perform its job. In the worst cases, excessive resistance could cause wire insulation to melt due to heat being generated. Open circuits will typically cause a component to not work at all, such as a light not turning on because of a bro- This diagnosis uncovers two issues: A short in a trailer circuit and battery drain caused by the brake control relay. by Barry Hoyland, Contributing Editor The Cal-Van Tools Amp Hound 2 allows us to read amperage on any circuit without needing to install the tester in series. While testing for battery drain during initial diagnosis, our tests determined there was no current drain at this time (Fig. 1, main image). After the customer had an opportunity to drive the trailer for a period of time to duplicate the original conditions, the amp draw test was repeated and showed a 2-amp draw. (Fig. 2, inset).
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